Process for the electrolytic deposition of gold-copper-cadmium alloys

ABSTRACT

THE ELECTROLYTIC DEPOSITION OF GOLD-COPPER-CADMIUM ALLOYS ACCORDING TO HEILMANN U.S. PAT. 3,056,733 IS IMPROVED BY INCLUDING SMALL AMOUNTS OF SILVER IN THE AQUEOUS ALKALINE CYANIDE BATH.

United States Patent US. Cl. 204-44 2 Claims ABSTRACT OF THE DISCLOSUREThe electrolytic deposition of gold-copper-cadmium alloys according toHeilmann US. Pat. 3,056,733 is improved by including small amounts ofsilver in the aqueous alkaline cyanide bath.

In Heilmann US. Pat. 3,056,733 (German Pat. 1,141,- 849) there isdescribed a process for the electrolytic deposition ofgold-copper-cadmium alloys from an aqueous alkaline cyanide bath bymeans of a periodically reversed current density using insoluble anodes.This process is characterized by use of a bath containing 1 to 3 grams/liter of gold as potassium gold cyanide, 5 to 15, preferably 8 to 13grams/liter of copper as potassium copper cyanide or sodium coppercyanide, 0.1 to 0.8 gram/liter of cadmium as potassium cadmium cyanideor sodium cadmium cyanide and 3 to 8 grams/liter of free cyanidecalculated as potassium cyanide. The bath has a pH of 9 to 11 and acurrent density of 0.5 to 1.5 a./dm. during the cathodic phase of 4 to20 seconds as well as a current density of 0.75 to 3.75 a./dm.preferably 1.0 to 3.0 a./dm. during the anodic phase of 0.5 to 2seconds. The ratio of cathodic to anodic current density is preferablyless than 1:15.

A disadvantage of the described process consists in that the permanentbright current density range is relatively small so that it can only beused for electroplating small and as much as possible simple formedparts. Besides the deposition of reddish coatings sets tight boundariesfor their film thickness and finally the roughness of the coating atgreater film thickness are increased.

Unexpectedly it has turned out that these disadvantages can be avoidedif one adds a small amount of silver to the bath. This addition can bein the form of potassium silver cyanide or other silver salts compatiblewith the rest of the bath composition. The concentration of the bath insilver should be between 0.01 and 0.1 gram/liter. This silver contentmust be maintained over the entire useful life of the bath that thesupplemental addition of silver corresponds to an amount of 0.2 to 2% ofthe content of gold and alloying metals.

Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1 An aqueous bath containing 1.5 grams per liter of gold aspotassium gold cyanide, 10.5 grams per liter of copper as potassiumcopper cyanide, 0.3 gram per liter of cadmium as potassium cadmiumcyanide, 0.05 gram per liter of silver as potassium silver cyanide and5.0 grams per liter of free potassium cyanide was electrolyzed with acur- Patented June 22, 1971 ice Percent Gold 74 Copper 15 Cadmium 10Silver 1 A portion of the alloying metals exists in the supplementaryadditive in the form of a simple, non-cyanide, in aqueous solution acidreacting salt, e.g. salts of sulfuric acid in order to keep the freecyanide content of the bath and the pH value within the necessarylimits. The silver content of the bath can be supplemented with theremaining metals or separately.

There are also obtained with film thicknesses of 20 or higher in arelatively wide brilliant current density range, highly lustrous,smooth, yellow to red about 18 carat gold coating of especially highhardness.

The conditions of operation are l to 3 grams per liter of gold aspotassium gold cyanide 5 to 15 grams per liter, preferably 8 to 13 gramsper liter of copper as potassium copper cyanide or sodium copper cyanide0.1 to 0.8 gram per liter of cadmium as potassium cadmium cyanide orsodium cadmium cyanide, 0.01 to 0.1 gram per liter of silver aspotassium silver cyanide.

3 to 8 grams per liter of free cyanide as potassium cyanide.

Current density of 0.5 to 1.5 a./dm. during the cathodic phase of 4 to20 seconds.

Current density of 0.75 to 3.75 a./dm. preferably 1.0 to 3.0 a./dm.during the anodic phase of 0.5 to 2 seconds.

The temperature can be between 60 and C.

The supplementary additive can for instance consist in two solutions.The first of these solutions contains 40 grams per liter of gold aspotassium gold cyanide, 0.5 gram per liter of silver as potassium silvercyanide and 10 grams per liter of copper as potassium copper cyanide orsodium copper cyanide. The second solution contains 3 grams per liter ofcadmium as cadmium sulfate or cadmium nitrate or cadmium acetate. Forsupplementation equal amounts of the two solutions are added to thebath.

What is claimed is:

1. In a process for the electrolytic deposition of goldcopper-cadmiumalloys from aqueous alkaline cyanide baths using periodically reverseddirect current, the steps which comprise electrolytically depositing agold-coppercadmium alloy from an aqueous cyanide bath maintained at a pHof 9-11 and containing 1 to 3 grams per liter of gold as potassium goldcyanide, 5 to 15 grams per liter of copper as potassium or sodium coppercyanide. 0.1 to 0.8 gram per liter of cadmium as potassium or sodiumcadmium cyanide, 0.01 to 0.1 gram per liter of silver as potassiumsilver cyanide and 3 to 8 grams per liter of free cyanide as potassiumcyanide, the duration of each cathodic phase being 4 to 20 seconds andthe duration of each anodic phase being 0.5 to 2 seconds and maintainingReferences Cited a current density of 0.5 to 1.5 a./dm. during thecathodic phase and a current density of 0.75 to 3.75 a./dm. duringUNITED f PATENTS the anodic phase 3,056,733 10/1962 Hellmann 20444 2. Aprocess according to claim 1 wherein the bath 5 concentration ismaintained by adding supplementary ad- GERALD KAPLAN Primary Exammerditives containing salts of gold, silver, cadmium and copper U S Cl X Rand wherein the silver is 0.2 to 2% based on the total of 75 165 t thegold and alloying metals.

